Controllable preparation and formation mechanism of monodispersed bulk nanobubbles in dilute ethanol-water solutions

Abstract

Ethanol-water mixing method has been widely used to prepare nanobubbles, however, in dilute ethanol-water solutions, the preparation of monodispersed bulk nanobubbles with high number density has not been achieved. Herein, a controllable bulk mixing (CBM) method is designed to fabricate monodispersed bulk nanobubbles at a low volume ratio of ethanol to water (less than 10:100), which can prepare high-number- density (at around 2 × 109 bubbles/mL) and high-stability bulk nanobubbles. Notably, after 9 days of aging, a considerable number of nanobubbles can still be captured by NTA technology. The formation and influencing parameters of the bulk nanobubbles in this system are also explored. Based on our experimental results, a plausible mechanism of nanobubble nucleation and growth at ethanol/water interfaces is proposed to understand the formation of bulk nanobubbles. A hypothetical model is established and as a result the Laplace pressure of bulk nanobubbles in dilute ethanol-water solutions is obtained. The Laplace pressure given by the surface tension might be less than 0.5 atm.